1. Chromosome abnormalities Ajith Sominanda Department of Anatomy Faculty of Medicine Peradeniya

2. Development of cytogenetic techniques to analyze chromosomes led to discovery and characterization of chromosome disorders (1950s)
Within years (from 1956), the cause of Down syndrome (47,XX/XY+21) Turner syndrome (45,X) and Klinefelter sysndrome (47,XXY) was established
Now more than 20,000 chromosome abnormalities have been reported but these conditions are very rare in the population
Chromosome abnormalities are a major cause for early pregnancy loses

3. Types of chromosome abnormalities
Numerical abnormalities
(Abnormal changes in the chromosome number in a cell)
Structural abnormalities
(abnormalities of the chromosome structure
Others

4. Failure of chromosomes to seggregate (move) during cell division : Non-dysjunction
Normal Gametes
Mono somic gametes
Nullisomic gametes

5. Non dysjunction Occurs with advancing age; especially maternal age
Maternal oocytes have a long delay between different phase of the cell division
With advancing age, spindle formation become defective and leads to non dysjunction

6. Gametogenesis in female and risk of non dysjunction

7. Gametogenesis in male

10. Numerical abnormalities
Aneuploidy
(loss or gain of one or more chromosomes)
Monosomies (loss of a single chromosome)
45,X - Turner syndrome (loss of one sex chromosome)
Monosomy of autosomes are incompatible with life
Trisomies (Presence of an extra chromosome)
Trisomy 21 (Down’s syndrome)
Trisomi 18 (Edward’s syndrome)
Trisomi 13 (Patau Syndrome)
XXY (Klinefelter syndrome)
XXX (XXX females)
XYY (XYY males)
Tetrasomies (Presence of two extra chromosome)

11. (Addition of one or more haploid set of chromosomes)
Polyploidy
(Addition of one or more haploid set of chromosomes)
Triploidy (3n =69)
Tetraploidy (4n =92)
Retension of polar bodies or fertilization with 2 or 3 sperms can lead to polyploidy
Tetraploidy ( =92)
Triploidy (46+23=69)
Triploidy ( =69) 23 23 23 23 23 23 46 23 23
Ovum polar body

12. Monosomies (loss of a single chromosome)
Turner syndrome
Karyotype is 45,X

13. Trisomies (Presence of an extra chromosome)
Down Syndrome Trisomy 21 (47,XX/XY+21)

14. Trisomies (Presence of an extra chromosome)
Edward syndrome
Trisomi 18 (47, XX/XY, +18)

15. Trisomies (Presence of an extra chromosome)
Patau syndrome
Trisomi 13 (47, XX/XY, +13)

16. Trisomies (Presence of an extra sex chromosome)
Klinefelter syndrome (47, XXY)
Slightly femine figure
Has low IQ and
Learning difficulty
Infertile

17. Trisomies (Presence of an extra sex chromosome)
XXX females (47,XXX)
Looks normal in phenotype
Slightly less IQ
Fertile

18. Trisomies (Presence of an extra sex chromosome)
XYY males
Tall
Aggressive
Low IQ and learning difficulties
Normal fertility

19. Structural abnormalities
Translocations
Deletions
Insertions
Inversions
Rings chromosmoes
Isochromosomes

20. Types of translocations

21. Insertion

22. Inversion

23. Mosaicism
is caused by an error in cell division very early in the development of the unborn baby due to chromosome abnormality

24. Chimerism
chimera or chimaera is a single organism composed of two or more genetically distinct cellspopulations from different zygotes